The present application relates to switching devices for use with fluids, either liquids or gases, and more particularly, to switching devices operated by fluid pressure.
Modern fluid sampling apparatus is designed to be accurate to a high degree. Many such devices depend upon the analysis of a discrete sample for their determination as to content. Often, accurate determination of the quantity of specific components is directly dependent upon the accuracy of the sample size. Gas chromatography is one example of such sampling and analysis apparatus wherein a fixed sample size is incorporated. To accomplish accurate sample injection into the analyzer, apparatus such as that shown in FIG. 1 is most often employed. An input for the sample gas is provided as well as an input for a carrier gas which is used to move the discrete sample into the analyzer. Appropriate valving must be provided in conjunction with a sample loop. The valving apparatus is first put in a position such as that of FIG. 1A wherein the sample gas is directed through the sample loop and thence out through a sample output. Simultaneously, the carrier gas is passed directly to the analyzer to purge out the contents of the prior analysis. When the analyzer has been purged by the carrier gas and the sample loop is full of sample gas, the valve is switched to the position of FIG. 1B. In this configuration, the sample gas is passed directly through the valve and to the sample output. At the same time, the carrier gas input is directed through the valve and into the sample loop, through the sample loop, back to the valve, and to the analyzer. As the carrier gas moves through the sample loop, the sample of gas contained therein is moved out of the sample loop and into the analyzer. The amount of sample gas moved into the analyzer, therefore, is fixed by the volume of the sample loop. Since such analyzers oftimes are used with very small samples, any leakage or lost volume in the valve contributes to inaccuracies in the readings obtained from the analyzer. Consequently, such prior art valving arrangements have commonly incorporated slider blocks or sliding cylinders such as in the apparatus of FIG. 1 wherein all connections are made into a fixed body. A slider block is mounted on the body such that when in a first position the inputs and outputs will be interconnected in one manner. When the slider block is moved into a second position, the inputs and outputs are interconnected in a different manner. In order to move the slider block between the first position and the second position, mechanical drive means as with fluid actuated pistons or such must be provided. To prevent leakage, the body and slider block assembly must incorporate various "O"-ring seals and the like. Such valves are, accordingly, large, costly, heavy, and require periodic maintenance.
Thus, it is the object of the present invention to provide an improved switching apparatus for use in the switching of fluid lines, particularly adaptable to gas sampling instruments, which is simple, light weight, can be miniaturized, and requires virtually no maintenance.